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BY THOMAS K GROSE

WHILE SUPPLIES LAST

Research engineers are finding new ways to produce more fresh water and to recycle what’s been used.

Once upon a time, water was not a worry in the United States. It was relatively cheap, generally plentiful, and easy to take for granted. No more. The world faces a growing water shortage, and the United States won’t be spared. An ongoing, extreme drought has already sucker-punched the country’s Southeast, causing interstate squabbles over dwindling resources. Up north, levels in the Great Lakes are dropping. In the West, the mighty Colorado River is likewise shrinking, as is Lake Mead, while the Sierra Nevada Mountains snowpack is melting at an alarming rate. All told, 36 states are projected to experience water scarcity between now and 2012. The Western states may experience drought for decades.

That’s a scary prospect, considering how vital H2O is to human existence — besides drinking it, we need it for hygiene, for growing and processing food, and for traditional and high-tech manufacturing and energy production. Worse, the many causes of water shortages, even man-made ones, aren’t easily controlled. They include global warming, rising populations, increasing industrialization in the developing world, pollution, and waste. And water doesn’t often accumulate where it’s most needed. For instance, 30 percent of the Earth’s freshwater supplies are in Asia, home to 60 percent of its population.

Forget the old solutions for easing shortages. We’ve pretty much dammed all the rivers we can. Pumping water hundreds of miles can be costly and use up ever-more-expensive energy. Aquifers are being tapped out. And as populations expand, there are limits to the extra water supplies that can be squeezed from conservation, water-efficient appliances and toilets, and use of partially treated wastewater for non-potable purposes.

So, are we doomed to an arid demise? No, say engineering academics working in water treatment and management. They’re convinced that science and technology will come to our rescue. “New, sustainable, affordable, safe, and robust methods to increase supplies and purify water can be developed and implemented to serve people throughout the world,” claims a March 2008 Nature article by six engineers led by Mark A. Shannon, a mechanical engineering professor and water expert at the University of Illinois at Urbana-Champaign.

“There are many more opportunities to combine water treatment and renewable energy than in the past.” —Michael Hightower, Sandia National Laboratories

Indeed, technologies are available to produce more fresh water and to clean and recycle what’s already been used. But much more research and development will be required before water again becomes abundant and affordable. Different geographical conditions — proximity to oceans, for instance — will dictate different responses to the coming scarcity. And while water’s basic composition is two atoms of hydrogen for every one of oxygen, scientists now recognize that it contains a variety of chemicals and differs from place to place, complicating water treatment.

COST-EFFECTIVE DESALINATION

One method for producing fresh water has been around for decades and is becoming more efficient. That’s desalination. Water covers around 70 percent of the Earth’s surface, but 97.5 percent of it is unfit for human consumption. It’s either seawater or brackish inland water. There’s as much brackish groundwater in the world as fresh water. Clearly, there’s great potential in separating the water and salt. A 2004 report by Sandia National Laboratories predicted that desalination will produce a “significant” amount of America’s water supplies.

“Water desalination is the future,” says Yoram Cohen, who heads the Water Technology Research Center at the University of California-Los Angeles.

Though still a drop in the bucket in relation to overall American water use — 148 trillion gallons a year — desalination use is growing. Between 2000 and 2005, use of desalinated water grew by 40 percent. At a 10 percent annual growth rate, desalination could yield 4 billion gallons a day by 2020. A big reason for the increase is that improved technology is making desalination less costly. In the past, a thermal process was used to separate water from salt. Saline water is boiled until it evaporates and leaves the salt behind; the salt-free water is reclaimed when the steam condenses. This sounds simple, but it’s very expensive, because it requires enormous amounts of power to work.

The technology of choice now is reverse osmosis (RO), which was developed by UCLA engineers in the 1960s and now is headed to capture 60 percent of the market. Essentially, water is pumped under high pressure through membranes that filter off the salt. It too requires a lot of electricity but not nearly as much as the thermal method. And advances in membrane technology and energy recovery methods have, within the past decade, made RO desalination much more cost-competitive. It’s now around $3 to $4 per 1,000 gallons. Traditional municipal water costs on average $2 per 1,000 gallons, but in many areas it’s rising — especially in communities needing to look further afield for fresh supplies. Las Vegas, for example, plans to pipe in water from northern Nevada, some 300 miles away. Conveying water great distances can ultimately be more expensive — and less energy efficient — than treating local supplies of sea or brackish water.

Research is underway to make desalination still more energy efficient. Yale University environmental engineer Menachem Elimelech is working on a desalination process called forward osmosis (FO) that uses only a tenth the energy of RO. Indeed, he envisions that the energy could come from capturing waste heat from power plants. FO, Elimelech says, can recover 75 to 80 percent of the water. Instead of pushing salt water through a membrane, Elimelech’s FO process sucks the water through using a draw solution of dissolved ammonia and carbon dioxide. That solution is then heated to remove the ammonia and CO2, leaving fresh water behind. Ideally, FO would work best with a new power plant designed to accommodate the process. “But,” he says, “it could be made to work with existing plants. We’re still working on that engineering. In five years, this could be something.”

THE PROBLEM OF WASTE

Besides energy use, desalination imposes other costs: Maintenance is expensive, because RO membranes eventually become fouled and need to be cleaned or replaced. That’s why Cohen says that desalination, though it’s been around commercially for nearly 40 years, is hardly a mature industry: “There is still a lot of room for development.”

An even tougher problem is effluent. Current RO technology collects, at best, around 55 percent of the water processed. That means quite a bit of briny concentrate is left behind. In coastal areas, it can be pumped out to sea. But inland, disposal of brine presents engineers with a major environmental headache. “It’s one of the biggest holdbacks,” admits Michael Hightower, a water expert at Sandia Labs. Sometimes it’s pumped into deep-Earth saline aquifers, but that requires a lot of energy, too. If much more water could actually be recovered and used, the amount of effluent would diminish.

Mark Shannon’s Center of Advanced Materials for the Purification of Water with Systems at Illinois forages through basic research looking for new ideas to treat water. One concept that intrigues him — though the technology for it does not yet exist — is this: Instead of forcing water through membranes to separate it from the salts, figuring out a means to suck salts out of a solution, leaving potable water behind. That would somewhat mimic nature, Shannon says, which draws off hydrated ions and leaves fresh water behind. “Total energy use,” he says, “would be far less.”

In their quest for a more efficient membrane, some researchers hold out hope of reducing the desalination problems of maintenance, effluent, and energy use all at once. Researchers are focusing on creating a new generation of membranes that require less force — and so less energy — yet produce more potable water and are more resistant to fouling and scaling. Hightower says the most efficient filter is the human kidney. If science could devise a membrane that works as well, there would be a three- to five-fold improvement in desalination efficacy.

NANOMEMBRANES, NEW FUELS

One promising avenue is nanotechnology. Researchers at the Lawrence Livermore National Laboratory and the University of California-Berkeley are developing filters that use carbon nanotube-based membranes on chips the size of quarters. They say it could reduce energy requirements by 75 percent. Back in L.A., Cohen and his team at UCLA are working on a process called “accelerated precipitation softening,” which is aimed at improving the desalination of brackish water so that 95 to 98 percent of the water is recovered, drastically reducing the amount of brine requiring disposal. The method calls for treating the brine to increase its acidity and de-mineralizing it, then putting it through an RO membrane again, to squeeze more sweet water from the concentrate.

A team led by James E. McGrath at Virginia Tech recently developed a treatment — a coating only a few nanometers thick — that makes membranes chlorine-tolerant. “That’s been a long-felt need in the industry,” he explains. Water has to be sterilized with chlorine before it can be desalinated, but chlorine can destroy a second, polyamid membrane used in RO. So, before it’s shunted through those membranes, the water has to be de-chlorinated. Afterward, it’s chlorinated yet again. Cutting out the de-chlorination and re-chlorination steps should save energy and money. Another possible solution — which is the focus of research by Thomas Davis, a chemical engineer at the University of South Carolina — is a process to separate valuable salts like magnesium and boron from brine. These have enough commercial value that their sale would more than cover the costs of disposing of the remaining effluent. Also, if production of biofuels from algae ever becomes widespread, that industry may create a market for desalination brine, Hightower says, because the algae grow in salt water.

Beyond membranes, researchers are also looking at saving fuel by linking desalination with renewable energy sources.

Alternative energy, for now, is often more expensive than power derived from fossil fuels. One variety, biofuels, requires substantially more water to produce than does gasoline. But if a company can produce and sell water, as well as power, the combination may prove economically sensible. “There are many more opportunities to combine water treatment and renewable energy than in the past,” Hightower says, especially if the plants are designed to do that from the start. Engineers at Texas Tech University are planning a $1 million pilot wind-powered RO plant in Seminole, a town in West Texas that will produce from brackish water 30,000 gallons of potable water a day.

TREATMENT AND REUSE

Aside from producing fresh water from the sea or brackish aquifers, great potential is seen in the recycling of wastewater, including sewage, industrial, and storm waters. Explains Shannon: “This is where technology comes into play. Water is water. Lots of dry areas are awash in water they’re typically not using. We just cannot keep thinking in the same way. We all use reused water, anyway,” since evaporated water returns as rain. It’s a concept that’s gaining appeal. Recycled wastewater capacity is increasing at a rate of 15 percent a year. Once consumers get used to the idea, it makes a lot of sense. For one thing, municipalities have wastewater collection and treatment facilities in place already, so the only new costs are extra treatment and distribution. It can be a cheaper option than desalination.

Indirect use of treated wastewater includes irrigation, industrial applications, and the cooling of power stations. Direct use is funneling the treated water below ground to recharge aquifers — some of which are running dangerously low — allowing the Earth’s natural filtration system to further cleanse it. When it’s pumped out, treated, and used again, “it’s not quite toilet to tap, but close,” Hightower says.

While recycling has long been accepted, its ability to purify water has been called into question because “our ability to detect low concentrations [of trace pollutants and pathogens] has also improved,” explains Edward J. Bouwer, an environmental engineer at Johns Hopkins University. Recycled water has been found to contain not only industrial and agricultural pollutants and pharmaceuticals but potentially cancer-causing toxins formed as byproducts when disinfectants, like chlorine, mix with natural elements in the water. Minute amounts of toxins may not pose a health hazard, but they can affect public perception of recycling. This is where Bouwer’s research — the mapping of chemicals found in water supplies combined with epidemiological studies to determine risk – comes into play. So far, he notes, there’s no evidence that recycled water has harmed anyone. But it’s research like his that will ultimately ease public fears.

New ways to clean water supplies that are clearly tainted with industrial pollutants, like petroleum hydrocarbons, are also being developed. One approach is bioremediation, the use of bacteria or plants that have a natural appetite for petroleum and essentially feed off of, break down, and render harmless oil-based pollutants.

Water tainted by arsenic — a highly toxic carcinogen — is also a problem in some areas of the United States, and more so in the developing world. But a new technology invented by a team of Lehigh University engineers led by Arup K. SenGupta, a civil and environmental engineer, removes arsenic from groundwater. The process, marketed under the name ArsenXnp, uses hybrid nanoparticles of lead throughout a polymer-based bead that are dispersed by an anion exchanger and absorb the arsenic. The ArsenXnp technology already purifies groundwater used by 300,000 people in nine states, as well as in such developing countries as India, Hungary, and Ecuador. In Eastern India, SenGupta’s original home, the technology has been used in 150 villages plagued by arsenic in well water.

Because of health fears about chlorine byproducts, other water-purification technologies have been developed, including treating water with ultraviolet radiation and ozone. But unlike chlorine, which continues to treat water all the way to the tap, UV and ozone treatments can be applied only at the processing plant. Shannon says what needs to be found are treatments that are as effective as chlorine but that don’t use chemicals. Shannon also hopes to see research into detection of viruses in water. While it is primarily a problem in the developing world, the United States is not immune to waterborne viral infections. In Milwaukee in 1993, some 403,000 people were sickened and more than 100 died when the city’s water supply was infected by Cryptosporidium parvum, a virus that causes severe diarrhea, stomach cramps, and fever. Shannon believes it’s possible to develop detectors that work like litmus paper and cost only pennies to produce.

Despite signs of a looming U.S. water shortage, the federal government has not made the search for solutions a priority, researchers complain. A National Research Council report in early 2008 said U.S. spending on desalination research had slid from $24 million a year to $10 million and was dispensed haphazardly. It recommended an increase to $25 million, overseen by the Office of Science and Technology Policy.

“It’s not a major [federal] initiative,” says Yale’s Elimelech, a member of the panel that produced the NRC report. Most of his own research funding has come from the U.S. Navy. If research money is in short supply, interest in the field on campuses is absolutely gushing — particularly among students interested in sustainability. A number of schools, including UCLA and the University of Florida, have set up centers dedicated to water research. Rather than creating a lot of new courses, many schools are instead augmenting engineering programs with more courses in biology and organic chemistry.

And these students are finding jobs in a fast-expanding water treatment industry — one needing increasing numbers of engineering graduates to make it work. “I cannot graduate students fast enough,” enthuses Benny Freeman, a chemical engineering professor at the University of Texas-Austin.

Those graduates who move into research have their work cut out for them. “Eventually, in 20 to 50 years’ time,” Bouwer says, “demand will exceed [fresh water] supply.” A health and economic crisis in the U.S. could be one result; elsewhere, it could spark war. Thousands of engineers are trying to prevent that from happening.